The present invention relates to labels for dry cell batteries. More specifically, the invention is directed toward a single ply battery label with a varnish surface that has geometric patterns along two edges to adapt to shrinkage of the film and provide a substantially continuous surface of varnish protectant for the rims of a dry cell battery. Throughout this application the term "rim" or "rims" will be defined to mean the outer corner surface at each end of the battery.
A dry cell battery has first and second terminals that have opposite polarity on opposing ends of the battery. The battery is partially encased with a nonconductive label that wraps around the outer circumference of the battery and extends longitudinally beyond the rims of the battery, defining openings for first and second terminals. Only the contact surface terminals of the battery are exposed for proper use of the battery.
If the film of the battery label is broken or cut through, shorting of the battery is possible. The rims and outer circumference of a dry cell battery must be protected, or the battery may short circuit. Battery labels insulate the battery cans. Also, the label may protect the product and user from leakage of the components of the can. Many dry cell batteries are disposable, and, even for those that are not, the reliability and expense of labels that provide appropriate protection and designate trademarks and origin of manufacture are significant factors in producing batteries.
Before application, labels are generally longer than the can of the battery at both ends. Labels are removed from release liners and wrapped around batteries with edges extending beyond the rims of the battery. The wrapped battery passes through a heating unit that heats the portions of the label that extend beyond the can. Being heat shrinkable, the extended edges of the label shrink around the rims of the battery. The shrunken label wraps around the rims of the battery forming a tight protective seal. Wrinkling or folding of the label along the rims can render the battery label visually unacceptable or less effective because the resistance to external destructive forces will be less.
Multi layer battery labels continue to function adequately for dry cell batteries. Single ply battery labels are generally less expensive to produce.
One such method includes the label shown in Patent Cooperation Treaty application number U.S. 96/10769, which was published Dec. 27, 1996. It shows a single ply label for labeling dry cell batteries formed of a transparent heat shrinkable polymeric film backing. It has third and fourth ends that extend beyond the opposed ends of the battery. An alkali resistant, electrically non-conductive, opaque pigmented layer is applied over the inner surface of the film backing. An electrically non-conductive, pressure sensitive adhesive layer is applied over the pigmented layer along at least the edges that are parallel to the axis of the battery.
Also, U.S. Pat. No. 5,292,566 shows the layer of metal moved from between layers of heat shrinkable film to between a heat shrinkable polymeric film layer and a layer of pressure sensitive adhesive. In the above PCT application, the applicant describes some problems of this embodiment. The bond of the metal to the polymeric layer is weak and the layer of metal is susceptible to cracking, which may penetrate the pressure sensitive adhesive layer and short circuit the battery.
Next, U.S. Pat. No. 5,190,609 describes a UV cured varnish for the top layer of polymeric film. This label has found limited acceptance because the coating has proven to be the weak link exhibiting poor abrasion resistance and resistance to environmental conditions.
It has therefore been found beneficial to produce a single ply battery label that provides insulation and protection without having weak links, problems with cracking metallization, and defects such as wrinkling and unacceptable visual aspects due to overlapping varnish when the film is shrunk on the rims of the battery. The label along the rims of the battery will have a non-wrinkled smooth continuous surface.